It is often necessary when drilling a bore hole to maintain or enlarge the diameter of the bore hole with second and subsequent passes of cutting components. This is necessary due to drill bit wear and gradual reduction in the gauge diameter of the hole. Also, certain materials being drilled can swell, which results in reduction of the bore hole diameter after the drill bit has past.
Reamers can be used in association with a drill bit to ensure that a bore hole is drilled to a constant diameter. A roller-type reamer has cutting components rotatably mounted. The roller reamer is commonly used in the drilling industry, one purpose being to ream the hole just behind the drill bit to maintain hole size. A roller reamer can also act as a stabiliser above the drill bit to stabilise the drill bit and drill string against the deviating tendencies encountered during drilling.
One problem with roller reamers is that under the conditions encountered during drilling, rock chips and other debris can build up behind the roller, which may jam or slow rotation of the rollers thereby reducing their effectiveness. Also, even under normal operating conditions, rotation of the rollers can also cause the roller to increase in temperature which further increases the stress on the rotating parts. Increased stress may cause those rotating parts to wear more quickly. This is a costly problem because the reamer will have to be brought to the surface, dismantled and reassembled.
The technique of reaming is a significant step in achieving the required diameter of the bore hole. Accordingly there is always a need for reamers with improved construction and longevity. It is an object of the present invention to reduce or eliminate some or all of the disadvantages of roller reamers discussed above, or at least to provide a useful alternative.